In modern portable wireless product designs, there is a continued effort to reduce size and improve the performance of radio frequency (RF) circuit components. One such component is the surface mount inductor which can be used as a resonator, as an RF choke, as a component in a hybrid filter, as well as various other applications known in the art. Modern manufacturing techniques require that the majority, if not all, of the electronic components found in an assembly be capable of being surface mounted in order to decrease manufacturing cycle time. Surface mount inductors can be formed using one of several known technologies including molded electronic component technology, wire wound chip inductor technology, and printed circuit board technology.
Molded inductors are typically formed of a helical wire coil molded over with any of a number of suitable thermoplastic materials, such as a polyetherimide which has a 10% fiberglass content, this material is sold under the tradename ULTEM 2100 by General Electric Company. Molded inductors are typically formed using a double shot molding or insert molding technique that provides a surface mountable part that can be packaged using tape and reel, which allows for robotic parts placement. A disadvantage associated with molded inductors is that the ends of the formed wires are still exposed in order to make electrical contact with an electronic circuit board. Controlling the extent to which the wires extend from the main body can be a difficult tolerance specification to maintain. It is also important that the main body of the coil be soldered down as close to the circuit board as possible in order to reduce microphonics. It would be a benefit to have a surface mount inductor that had no extending wires which would allow it to be soldered flush against a circuit board.
Another issue associated with today's molded inductors is that the plastics used tend to break down at temperatures above 220.degree. Centigrade. (.degree. C.). This can be an issue in manufacturing processes that need high temperatures (usually in the range of 230.degree. C.-240.degree. C.) to do a reliable reflow of electrical components on a substrate. A surface mount inductor that could be reflowed at high temperatures without deformation or breakdown would improve the reliability of the component as well as ensure an improved electrical contact between the component and the circuit board.
Another disadvantage associated with molded inductors is that multiple process steps are involved in the formation of these coils including winding the wire, performing the overmolding process, and a thin film plating procedure. These multiple processes are usually performed at different manufacturing facilities. Using a multi-process such as this can be expensive and drive up manufacturing costs. It would be desirable to form a surface mount inductor using a single process.
Other surface mount inductors known in the art include multiple "turn" and spiral patterned inductors formed on substrates, such as fire retarding glass epoxy (FR4) or ceramics. A disadvantage associated with today's spiral/multi-turn inductors is that they tend to have low inductance values and low quality factor (Q). In order to achieve high Q (approximately &gt;100) and high inductance (approximately &gt;10 nanohenries) the form factor of these components becomes too large for portable product applications. Ceramic substrates are costly and do not lend themselves well to being stacked due to alignment issues. Multilayer ceramic inductors are also prone to dendrite growth and silver migration. While substrates such as FR4 can be stacked, the Q tends to decrease as the part size increases. High Q components are critical to meeting high performance product specifications. A patterned inductor having high inductance values and high Q would be beneficial in terms of meeting electrical specifications.
While most surface mount coils can be tape and reeled, they still require proper orientation as there is typically only one "surface mountable" side. Thus, wire wound chip inductors require that a turn be completed down to the surface mountable side which limits the range of available inductor values. It would be a further advantage if a surface mountable inductor could provide high Q, high inductance values in conjunction with smaller incremental tuning ranges. A surface mount inductor that is surface mountable across all sides would make the component easier to package as well as easier to place robotically.
Accordingly, there is a need for an improved surface mount inductor that can be manufactured using a single process technique without the use of formed wires. It would be a benefit if such a part could be surface mountable from all sides in order to ease packaging and component placement. It would be a further benefit to provide a surface mount inductor that provides smaller incremental tuning ranges.